I have a 2000 chevy blazer 4x4 with this auto climate control thing. Everything works fine till it recently got cold here and I start using the heater. I bought the truck early this year like around april 08, this is my 5th s-10 but first s-10 blazer,rest have been pickups. Well the heater will only work at the max level say the switch is all the way over the the red hash mark, if I lower to anything else I get cool air, I won't say cold but cool. I have read of some tranny fluid backing up in a vacuum line []OMG could it be that, I was hoping for a bad switch, thermostat/thermocouplle tempcontrolor something simple, guess I be out of luck. Any ideas from the powers to be out here? anyone experienced the same problem and can lead me down the road to a fix? system worked fine all summer long in regard to the A/C and its temperature control, its just the Heater its either all or none

 

Sounds like a heater control valve issue to me-but as the newer units are all vacuum controlled I would check vacuum/electric functions of the HVAC system, not always simple on these units! Refer to a factory type manual or a well knowledged GM tech for insight-I assume you already did the usual coolant/t-stat checks... let me know step66

 

The temperature blend door is electric. It is possible that this door is either stuck between modes or is not closing all of the way.

Here is the diagnostic procedure for "heating insufficient":

 

I haven't done any test yet just been reading what others have experienced, and was possibly looking for a quick fix, doesn't look as if I will get one and I'll need to invest in some good tech manuals I bought this blazer from the orginal owner in April this year its in great shape, loaded out with only 51K miles on it for $5500.00 I thought I scored a great buy plus the heated leather seats are awesome after a hard days ride hauling the ATV's back from the mountain. heater control valve?? and electric door?? first I have heard of these terms all 4 my S-10 pickups I never had a problem with anything except one oxgyen sensor put 100K+ miles on each.

 

The charts above will lead you to the proper conclusion, but by all means, get the appropriate tech manual.

I could throw some idea out there, but unless you verify it with the proper diagnostic steps, it really is just throwing something out there.

 

Just signed up a minute ago after looking to solve an issue. This Thread comes close.

My daughters '99 S10 has heat the only thing I am having a problem with is that the air flow through all the vents do not change as I go from Defroat to Lower vents. Basically the Vents are not opening and closing to change the air flow. I looked at the PDF's that were provided and being new to teh S10 world, I still don't know where to find what I'm looking for.
I am extremely Mechanically inclined , I maintain my other vehicles 100%. I just need to be pointed in teh right direction on this " New" Blazer.

 

Have a similar issue with my 2002 s10 Blazer. No heat at idle, too much while driving. Suspects are bad water pump, slipping belt, clogged (partial) heater core. I can get hot air out of vents by revving engine in park also. Engine temp is ok, fluid levels ok. Also, does the heater system control the temp of the air by mixing with outside air as opposed to controlling the flow of hot water to heater core? Finally, when the dash switch is set for dashvent/floor why does the A/C compressor cycle on and off?

 

The Fan operates fine. The Heat is good, it's just the selector appears to not ...well... select.

Is there a Vacuum line on the engine that controls the Vents? I am brand new to this Vortec V6 All I have done in the few hours my daughter was home was check the Coolant level and oil. And it was a quick drive in the rain when this Heater/defroster showed itself. Along with the rear wiper motor only pushing the Wiper halfway up the window.

 

Sounds like the mode selector on the dash might be bad.Need to see if you are getting vacum to the selector switch. Got to take the dash apart to get to the switch.Or see if you are getting vacum to the hoses located up by your brake booster.(Small vacum hoses in front of brake booster)